Mayoral hopeful Bill Thompson sat by silently as a guest at a campaign event loudly called City Council Speaker Christine Quinn a “whore” who could “kiss my ass,” The Post has learned.

The slur was made by Sean Kavanagh-Dowsett, the co-owner of the restaurant Tea and Sympathy, at a public campaign event for Thompson held at the eatery on Wednesday morning, according to audiotape of the event and the recollections of two witnesses.

The tape, which was provided by Mayor Bloomberg’s re-election campaign, reveals British expatriate Kavanagh-Dowsett and his wife, Nicky Perry, discussing the perils for small businesses along with other Village entrepreneurs.

As Perry was slamming Quinn as “ignorant” to the needs of small-business owners, her husband interjected, “She’s a whore, and you can quote me on that!”

Eight to 12 people were at the restaurant for a roundtable discussion featuring Thompson, the city comptroller and the presumptive Democratic nominee for mayor.

The tape does not record Thompson saying anything to denounce the remarks, and two attendees told The Post that they had no recollection of the comptroller decrying Kavanagh-Dowsett’s language.

One witness said Thompson laughed with discomfort and shook his head while looking at an aide, and covered his ears for a brief moment.

Asked why he didn’t say anything, Thompson’s campaign said, “Bill has great respect for Speaker Quinn and believes the comments made yesterday — at a forum open to the public — were inappropriate and offensive.”

Kavanagh-Dowsett told The Post: “I don’t recall saying that specifically. If I said that in any way, Bill Thompson certainly did not endorse that in any way, shape or form.”

But Kavanagh-Dowsett declined to apologize, saying he dislikes Quinn, a Democrat, because of her close working relationship with Bloomberg, whom he views as anti-small business. Quinn declined comment.